Device-to-device (Device to Device, D2D) communication refers to a manner in which user equipments communicate directly with each other instead of using a base station. A D2D technology can play a part in relieving a burden of a macro network and increasing a communication rate between user equipments. To implement D2D communication, user equipment needs to discover other user equipment that can perform D2D communication.
User equipment transmits a discovery (Discovery) signal by using a discovery (Discovery) frame, so that other user equipment can discover the user equipment, so as to perform D2D communication. Specifically, there is a periodic discovery frame, and the user equipment may send the discovery signal in the discovery frame. Each discovery frame may be divided into time units in terms of time, and each time unit may be divided into frequency units according to a same rule. In this way, the discovery frame used to send the discovery signal may include multiple frequency-time units (which may also be referred to as frequency-time positions), and each frequency-time position is indicated by using (i, j), where i indicates a frequency unit (which may also be referred to as a frequency domain position), and j indicates a time unit (which may also be referred to as a time domain position). The discovery frame may be embedded into a system, for example, may be embedded into a system frame of an LTE system. Such embedding may be continuous or discontinuous in terms of time, and may be continuous or discontinuous in terms of frequency. Bandwidth of the embedded discovery frame may occupy full system bandwidth, or may occupy partial system bandwidth. If two or more user equipments send a discovery signal always at a same time domain position in a same discovery frame, these user equipments cannot discover each other.
In addition, it is expected that some preset info/nation related to a discovery signal is sent at the same time when the discovery signal is sent. In the prior art, a method for sending the preset information is modulating the preset information into a discovery signal, but this consumes system resources. Another method is using a frequency domain position to indicate the preset information, but using a frequency domain position to indicate the preset information is limited by system bandwidth.